1. Technical Field
The technical field relates to a display device and, more particularly, to a display device and a driving method thereof.
2. Discussion of the Related Art
Display devices typically use cathode-ray tubes (CRT). Presently, much effort has been made to study and develop various types of flat panel displays, such as liquid crystal display (LCD) devices, plasma display panels (PDP), field emission displays, and electro-luminescence displays (ELD), as alternatives to CRT. In particular, LCD devices have been widely used. LCD devices typically provide high resolution, light weight, thin profile, compact size, and low power supply requirements.
Generally, an LCD device includes two substrates that are spaced apart and facing each other with a liquid crystal material interposed between the two substrates. The two substrates include electrodes that face each other such that a voltage applied between the electrodes induces an electric field across the liquid crystal material. The light transmissivity of the LCD device can be changed by adjusting the intensity of the induced electric field to change an alignment of the liquid crystal molecules in the liquid crystal material. Thus, the LCD device displays images by varying the intensity of the induced electric field.
FIG. 1 is a block diagram of an LCD device according to the related art.
As shown in FIG. 1, an LCD device may comprise a liquid crystal panel 130, a gate driver 120, a data driver 110 and a gamma reference voltage generator 100.
A plurality of gate lines GL1 through GLn are extended along a first direction and a plurality of data lines DL1 through DLm are extended along a second direction, where n and m are natural numbers. The gate lines GL1 through GLn and the data lines DL1 through DLm cross each other to define a plurality of pixel regions. A thin film transistor T is disposed in each pixel region and connected to the corresponding gate and data lines. A liquid crystal capacitor CLC is connected to the thin film transistor T.
The gate driver 120 may include a plurality of gate driving integrated circuits (ICs) and sequentially supplies gate voltages to the gate lines GL1 through GLn. The data driver 110 may include a plurality of data driving ICs and supplies data voltages by one horizontal line to the data lines DL1 through DLm.
The gamma reference voltage generator 100 supplies a plurality of gamma reference voltages to the data driver 110 to generate the data voltages.
An image displayed by the LCD device may have 2k gray levels (where k is a natural number). Accordingly, where a data signal (having “k” bits) is supplied to the data driver 110, the data voltage outputted from the data driver 110 may also have 2k gray levels. Thus, to display an image with 2k gray levels, the data driver 110 may use a digital-to-analog converter (DAC) to generate 2k gray level voltages and to convert the data signal into the corresponding data voltage.
FIGS. 2A and 2B are block diagrams of data voltage generating circuits of a related art LCD device.
As shown in FIGS. 2A and 2B, the data voltage generating circuit includes a gamma reference voltage generator GR in a printed circuit board (PCB) and a DAC in a data driving IC D-IC.
The gamma reference voltage generator GR of FIG. 2A may include a gamma reference serial resistor string, where a plurality of resistors are arranged in series between a source terminal Vcc and a ground terminal. The gamma reference serial resistor string may divide the source voltage to output a plurality of gamma reference voltages VREF0 through VREF10.
The gamma reference voltage generator GR of FIG. 2B may include a plurality of gamma reference serial resistor strings. As shown, each gamma reference serial resistor string has two serial resistors, and the gamma reference serial resistor strings are arranged in parallel. Each gamma reference serial resistor string divides the source voltage and outputs the corresponding gamma reference voltage VREF0 through VREF10.
The DAC may include a gray level serial resistor string, where a plurality of resistors are arranged in series. The gray level serial resistor string is supplied with the gamma reference voltages VREF0 through VREF10 and may further output 2k gray level voltages V1 through V2k. Among the 2k gray level voltages V1 through V2k, the DAC selects the gray level voltage corresponding to the gray level of the data signal Ddata and then outputs a data voltage Vdata.
The DAC may require multiple gamma reference voltages since liquid crystal panel property and liquid crystal property when driving the LCD device may be different from those when designing the LCD. In other words, if the two properties are the same, the DAC outputs the gray level voltages that achieve a desired gamma curve of the liquid crystal panel by using the two gamma reference voltages VREF0 and VREF10. However, in reality, because such properties are sometimes different, the DAC may require multiple gamma reference voltages to achieve the desired gamma curve. Currently, the number of gamma reference voltages is about 9 to 11.
As the DAC requires multiple gamma reference voltages, there may be some problems. As explained previously, the gamma reference voltage generator may be disposed in the PCB and the DAC may be disposed in the data driving IC. Thus, to connect the PCB and the DAC, a flexible printed circuit board (FPCB) having multiple transfer lines for the gamma reference voltages is used. Additionally, the gamma reference voltages should be supplied to each data driving IC. Therefore, as the number of the data driving ICs increases, the FPCB will have a larger size and more transfer lines for the gamma reference voltages.
Also, as the number of the gamma reference voltages increases, the gamma reference generator will need more circuit elements. Thus, where a related art LCD device has multiple gamma reference voltages to achieve the desired gamma curve, the related art LCD will also have an increased product cost.
Further, as the related art LCD device may have one gray level serial resistor string, the gamma curve will be fixed after the LCD device is completed. Therefore, various gamma curves can not be achieved according to the need of the user or manufacturer.